1. Field of the Invention
The present invention relates to an external circulation type ball screw, and more particularly to an external circulation type ball screw with a noise-reduction structure.
2. Description of the Prior Art
Referring to FIG. 1, a conventional external circulation type ball screw comprises a screw 11 with a helical groove 111 in its outer surface, a nut 12 with a through hole 121 for passage of the screw 11, a return member 14 with a return path 141, and a plurality of rolling elements 15. The through hole 121 is provided in its inner surface with an inner groove 122 which cooperates with the groove 111 to form a load path 13. The return member 14 is disposed at on outside of the nut 12, the return path 141 is in communication with the load path 13, and the plurality of rolling elements 15 roll within the load path 13 and the return path 141. Such conventional external circulation type ball screw has the following disadvantages that need to be improved:
Since the return member 14 is disposed on the outside of the nut 12, and the noise of the ball screw mostly comes from the rolling elements 15 impacting a corner 141a of the return path 141 and rolling against the inner surface of the return path 141, that is to say that the noise source is exposed to the outside, which will cause a lot of noise.
Some other return members of the ball screws, such as disclosed in U.S. Pat. Nos. 5,373,755, 5,653,145 and US Publication No. 20080127764, are fixed by a covering plate and fasteners to reduce the vibration caused by the rolling elements impacting the return members at high speed. However, the high-frequency noise caused by the rolling elements at the corner of the return path still comes out.
And some other return paths of the ball screws, such as disclosed in U.S. Pat. Nos. 5,974,908, 6,668,672 and JP Pat Nos. 2007247720, 2005308081, 2004156767, 2004116688, and 2002276764, are completely covered by a fixing member, or even interiorly provided with vibration damping material to reduce the high-frequency noise caused by the rolling elements impacting the corner of the return path. However, the fixing member is not designed with any noise-absorbing structure, and the only noise-reduction measure is the wall thickness of the fixing member. The problem is that fixing member cannot be thick enough to provide an ideal sound-proof effect because it is restricted by the outer diameter of the screw.
The present invention has arisen to mitigate and/or obviate the afore-described disadvantages.